Conventional manufacturing technologies for semiconductor integrated circuits and flat panel displays may include processing of silicon wafers and glass panels, often referred to as substrates, in fully automated vacuum cluster tools. A typical cluster tool may include a circular vacuum chamber with load locks and process modules connected radially to the circumference of the chamber in a star pattern. The tool is typically serviced by a robotic manipulator (robot) which is located near the center of the chamber and cycles the substrates from the load locks through the process modules and back to the load locks. Another robot may be located in an atmospheric transfer module which serves as an interface between the load locks of the vacuum chamber and standardized load ports serviced by an external transportation system.
A conventional vacuum environment robotic manipulator typically includes a drive unit and one or more arms actuated by the drive unit. The drive unit often houses rotary motion axes, which are necessary to actuate the arm(s), and a vertical lift axis that allows the arm(s) to access stations at different elevations as well as to pick/place substrates from/to the stations. Conventional arm designs may include telescoping, SCARA-type, and frog-leg mechanisms.
In some applications, a vacuum robotic manipulator is required to replace a processed substrate with a fresh substrate. This operation, typically referred to as a substrate exchange, often directly affects the throughput performance of the cluster tool, i.e., the number of substrates processed by the tool per hour. In order to complete a substrate exchange operation, a single-end-effector robotic manipulator typically picks the processed substrate from the workstation, places it to a specified location, picks a fresh substrate from another location, and places it to the workstation. This sequence typically requires a total of thirteen discrete moves. The number of moves, and thus the substrate exchange time, can be improved substantially by utilizing a robot with two or more end-effectors, e.g., as disclosed in U.S. Pat. No. 7,891,935 incorporated herein by this reference. In this case, the robot picks the processed substrate by one end-effector and replaces it by a fresh substrate readily available on another end-effector, thus reducing substantially the number of moves on the critical path.
The drawback of some robots with two or more end-effectors may be the two or more arms that carry the end-effectors are coupled and may not be able to perform independent rotational and vertical moves. Considering the above described fast swap operation as an example, the arm with the processed substrate needs to wait for the arm with the fresh substrate to complete the place operation before it can start to move to another station.